With the recent chapter, it seems that Sage Mode or senjutsu is the only way to harm Obito's current form. This totally makes sense since the Juubi is like the Nature itself. But I doubt that Naruto's Base Sage Mode is gonna be enough to deliver the finishing blow. Also Kishi can't just cast aside Kurama because he plays a big role for the story. Naruto would have to harness all of his powers to defeat Obito, and to do that he would have to combine his two powers.